Although air conditioning has long been known and used with automotive vehicles, it was first provided in expensive high powered luxury cars where the added drag and power loss caused by engine driven accessory, and the poorer fuel economy that resulted therefrom, were of no real concern.
Over the years, as the popularity and availability of air conditioning increased, so too did the size and horsepower of most engines used in lower priced cars, and since fuel costs remained low, there was still no concern for the loss of power and fuel economy that came from having air conditioning in vehicles.
In Europe and elsewhere, where smaller cars and higher performance have long been important, and air conditioning in smaller luxury cars has become increasingly popular, particularly for exporting to this country, some efforts have been made to cut-out or switch-off the air conditioning during peak power demands of the engine. But little thought or concern has been given to the economy and fuel savings that might also be obtained in doing so.
Generally, some sort of switching device has been proposed whereby the magnetic clutch for the air conditioner, which is normally temperature or pressure controlled, is deactivated when the vehicle accelerator pedal is pressed to the floor, as in a vehicle passing situation. And either a simple on-off switch or a manifold pressure responsive switching device has been suggested for such purposes.
Although the accelerator pedal actuated on-off switch has its advantages in plain simplicity, it will be appreciated that this type of arrangement allows for no variations and is really available only to obtain a full power condition. Full power not fuel economy is the only concern.
In using some type of pressure responsive switching means, the air conditioner can be made to cut-out at other than full power and maximum load conditions. However, this is normally a pre-set factory determination and consequently hill and mountain climbing conditions, with different loads, in different cars, will effect when the air conditioner will or will not cut-out and no ready adjustment is available for extremely hot weather conditions when more frequent use of the air conditioner may be desirable, despite power and economy losses.
Another consideration frequently made in using air conditioners with smaller engines, is the need for a faster idle, when the air conditioner is operative, so that the car will not stall out as a result of added engine load while the air compressor is operating.
Usually the fast idle is obtained by a solenoid that is active when the air conditioner is turned on and which is effective in holding the idling cam to a fast idle setting. But, in using this, it is obvious that the fast idle is obtained whether the compressor clutch is engaged or disengaged by its internal switching devices. Obviously, to improve fuel economy, the fast idle should only be used when the compressor clutch is engaged.